Chaplinsky v. New Hampshire was a court case that happened a long time ago in 1942. In this case, a man named Chaplinsky said some mean words to a police officer in the street. The police officer did not like what Chaplinsky said and arrested him.
Chaplinsky went to court and argued that he had the right to say whatever he wanted because of freedom of speech. However, the court said that sometimes people can't say whatever they want if they are saying things that could cause harm.
This is called the fighting words doctrine. The court said that Chaplinsky's words were fighting words because they were meant to start a fight and could hurt the police officer's feelings.
In summary, the court said that even though we have freedom of speech, there are some things we can't say if they are meant to cause harm or start a fight.